Definition: Patients with persistent atrial fibrillation will be enrolled in this trial. All patients will be required to be in atrial fibrillation on the day of the procedure. Standard pulmonary vein (PV) isolation will be performed. Patients will be enrolled in the trial if they remain in atrial fibrillation after bi-directional block is obtained in the left and right sided PVs. At this point, patients will be randomized to receive 0.25mg of IV ibutilide or a placebo (normal saline). Patients will then undergo additional ablation with areas of complex fractionate electrograms (CFE) being targeted. The duration of additional CFE ablation and use of additional non-PV ablation (i.e. placement of linear lesions) will be left to the discretion of the operator. Patients will be followed for 1 year. The primary outcome assessed will be freedom from AF at 1 year.